That wasn't always the case.
Toilets in the USA used to mainly be washdown bowls. It was when they started using less water that they added the siphon jet to add performance to the flush.
There are still some models sold in the US that are washdown, but fewer and fewer.
In the US, because we've always had so much water, we're used to using it.
It's common courtesy to leave a clean bowl for the next user.
I believe that in other parts of the world, they don't worry about that.
Here, if there is anything left in the bowl, they will flush again to make sure it's clean.
We tend to take showers every day too.
We use more water per capita than anywhere else in the world.